Dynamic difficulty is a terrible idea. It reduces the potential difficulty-space of the game to two basic cases: Always too easy and always too hard. It means that if you lost, it's because the game chose to make you lose, not because of an effect on your choices, and if you win, it's because the game chose to let you win, not because of your skill.
Every couple of years I'll play a game with this new, innovative idea, and it's still the same story. It's sort of fun for a bit, until your brain catches up and realizes that as meaningless as most games are, this one is even more so. It's not a new idea and if it were going to work, it would have been made to work by now: http://www.intellivisiongames.com/bluesky/games/credits/spac...
(No, there is no in-between "just right". Simple control theory shows how you can't hover at the "just right" point; as you are at "just right", the system must dynamically adjust the difficulty above your level (or you even just hit a bad patch) and cause you to fail, at which point you're back at too easy. There's nowhere near enough data to get to "just right" even in theory.)